1. Field of the Invention
The invention relates to an electric power steering device.
2. Description of Related Art
As an electric power steering device applying assist force to a steering mechanism, an electric power steering device as disclosed in Japanese Patent Application Publication No. 2004-314770 (JP 2004-314770 A) is known. In the electric power steering device, a motor is arranged in parallel to a steered shaft and the output from the motor is applied as assist force via a transmission mechanism including one set of pulleys and a belt.
It has been generally known that, in this type of electric power steering device, an operating sound is generated when the set of pulleys and belt is operated and their teeth are meshed with each other. How to reduce such operating sound is regarded as a matter to be addressed.
For the aforementioned electric power steering device, one technical solution to reduce the operating sound is to spread the clearance between the pulley tooth and the belt tooth when they mesh with each other (referred to as “meshing clearance” hereinafter). However, if the meshing clearance between the pulleys and the belt is spread, tooth skipping may occur between the pulley teeth and the belt teeth more frequently, which is a new matter to be addressed.